Control mechanism



June 25, 1946.. G. A. SHORT CONTROL MECHANISM Filed Oct. 22, 1943 2Sheets-Sheet 1 //v1//vr0/? GEORGE 45/1021" BY f/yw MW ATTORNEYS June 25,19460 a sH T CONTROL MECHANISM Filed 001;.

22, 1945 2 Sheets-Sheet 2 INVEN TOR 5EOA=6E A. 5/1027 ATTORNEKS PatentedJune 25, 1946 CONTROL MECHANISM George A. Short, Cleveland, Ohio,assiznor to The Hotatream Heater Company, Cleveland, Ohio, a corporationof Ohio Application October 22, 1943, Serial No. 507,250 3 Claims. (Cl.238-46) 1 This invention relates to control-mechanism, such as is usedfor the control of furnaces, boilers, hot water or steam heatingequipment, or the like, by regulation of the draft, fuel feed'or the 7like, by or in accordance with variations in some suitable factor ofboiler or furnace operation, such as temperature, pressure, flow or thelike. The invention is an improvement upon that shown, described, andclaimed in the patent for Pressure controller, No, 2,304,802, grantedDecember 15, 1942, to Morris W. Crew.

In said patent the control is responsive to changes, for example, in thesteam pressure, which become eileotive to control a suitable operatingmotor which produces a correcting influence upon the boiler, such as byoperation of a draft damper. When a correcting effect is re quired orcalled for it is not produced either sud-= denly or continuously tocompletion, but by pro tracted step control, or in other words, by aseries of equal short increments or steps repeated and distributed atregularly recurring intervals over a fairly long period of time in! fullcorrection is completed or the opposite correcting efiect is celled for,whereupon the control system operates reversely or iznthe otherdirection.

One object of the present invention is to provide an improved controlsystem of this general type, so constructed and arranged as to be sensltive to comparatively small variations in the controlling function, suchas steam pressure, and which nevertheless is operative to produce allnecessary correcting effect with considerable recluction in the totalswing or maximum variation in the variable boiler function incident toor con= sequent upon this kind of boiler control.

Another object or the present invention is to improve the controlmechanism or said prior patout by the inclusion of means adapted, when acorrecting effect is called tor, and entirely regardless of the positionof the controlled device at the time, to introduce, ahead of theprotracted or step control, an immediate substantial adjustment of thedevice to be controlled, resulting in a. prompt substantial correctingeffect in boiler operation, but usually short of the total correctionnecessary, followed by sufllcient gradual, protracted, or step control,until reverse operation of the controlling equipment is called for.Still another object of the invention is to provide an improved controlsystem of this kind in which, upon a demand for it, effective operationof the protracted control means is delayed or withheld pending promptproduction of a substantial correcting influence upon the control ill) 2system in the right direction, whichever that may be Another object isto provide an improved control system of the character described, whichnot only tends to maintain the desired boiler function, such as steampressure, within a narrower zone or range of variation than heretofore,but which also is fully self-accommodating to variations in boiler load.

Further obie-cts 01' the invention in part are obvious and in part willappear more in detail hereinafter. I

In the drawings Fig. 1 is a diagram conventionally illustrating theinvention, applied for boiler control by actuation oi a damper; and Fig.2 is a diagram graphically illustrating operation of the control systemand its effect upon boiler oper ation.

Experience in practice with control systems of this kind shows thatwhen, upon a call for a correcting efiect, lull correction is produced.without delay, the control system is constantly hunt ing, as it were.lit is unreliable and unstable in the sense that the controlled device,such as a damper, is always moving to one Ofllh'i other of its extremesoi movement, or is in one of those extremes, and the boiler function,such as steam pressure, fluctuates rapidly and widely.

0n the other hand, when the correcting effect is protracted or isdistributed over a fairly long period, such as to or ill minutes, as insaid prior patent referred to, the gradual application oi thecontrolling efiect may succeed in more or less stabihalng the operation.The controlled device, such as a damper, may float or become more orless stabilized in an intermediate position, but nevertheless the swingin the boiler iunctlon is still undesirably large. For example, in onespecific instance, when the control is set to operate on a fluctuationof pound in steam pressure in either. direction from normal, the actualtotal maximum swing of pressure may he as much as 6 pounds or more.

The present invention is designed for use in those cases where inordinary use the variation in load demand or in the production oicombustion effect is such that the function to be controlled, such asboiler steam pressure, tends to vary considerably more than the amountnecessary to produce a, correcting effect. In other words, the inventionis applied, for example, where the control system is set to operate on afluctuation of /a pound of steam pressure in either direction from thenormal and yet boiler pressure actually may tend to swing over a totalrange of 6 to 10 pounds or more.

According to my invention, for the purpose of maintaining the functionto be controlled, such as boiler pressure, more nearly uniform, or toprevent undesirably wide swing in the boiler function, my control systemis so arranged that upon any demand for a correcting effect, no matterwhat is the position of the controlled part, that effect, in the properdirection, is immediately produced to a material exent, to-wit, to asmuch as 25 to 50 or more per cent of the total possible correction, thecontrolling system thereafter continuing to function, with a correctingeilect still in the same direction, but protracted or distributed overan extended period of time. The initial substantial correction is madeimmediately, in one step, and is assumed to extend over a relativelyshort period, such as a matter oi say seconds. The succeeding moreprotracted correction may be either continuous, or may occur by steps asin said prior patent referred to, but in either case is protracted ordistributed over or minutes of time. In either case the promptsubstantial correction immediately tends to change the combustion rate,either up or down, so as to produce steam in the specific form beingreferred to, either faster or slower as may be desirable. But this firstcorrecting eflect usually is not sufllcient to stabilize the boiler.That is accomplished by the subsequent more protracted correctingeffect, which is distributed over a soulcient length of time to enablethe change in the operative condition of the burners or boiler toreflect back upon the control system and stabilize it, in due course,according to the nature of the ori inal source of the demand forcorrection.

For convenience the system will be described as contemplating the moreprotracted latter portion of the correcting eifect as produced by stepcontrol, according to said prior patent, although the invention is notso limited.

The control system of the present invention is of electromechanical formin that in the specific form chosen for purposes of illustration and notin any sense of limitation the control system includes electric circuitscontrolling electric motors which mechanically operate switches andother boiler controlling members. Such electric equipment may be used tocontrol a furnace or boiler draft damper, a fan used for draft purposes,stoker speed, such as the speed of a chain grate stoker, fuel supplysuch as the position of the valves of oil or gas burners, or theposition of burner airports or dampers therefor, or other type of fuelbed control, or even an electric heater of resistance or other type usedto produce heat for similar purposes. These devices, by variation oradjustment, all affect the rate of heat production in such a manner asto increase or decrease steam pressure, steam temperature, steam flow,air temperature, or some other function of furnace or boiler operation.

In the particular arrangement chosen for purposes of illustration steampressure has been selected as the controlling function. A conduit ll,communicating with the steam I l of the water tube boiler i2conventionally shown, communicates with a suitable servomotor I2including a movable abutment IS, the motion of which is utilized toproduce a controlling eilect upon the controlling system to bedescribed.

Said system includes an operating motor A, the shaft of which isconnected, a by chain H, to operate a damper in a pipe [2a connected to4 the fire box [2b, the position of which damper controls the flow ofair or gas through the combustion chamber and consequently the rate ofheat production.

The controlling system includes two electric motors or motor units B, C,as well as electric circuits including said motors and a series ofswitches marked respectively S1, S2, S3, S4, S5, Se, Sea, S7, S75.

Motor A is a reversible motor, or motor unit, including r ducing gearingturning in one direction to close and in the other direction to open thedamper 15.

Motor or motor unit B is unidirectional and operates continuously. Itincludes reducing gearing so that its operating shaft i6 turns slowly,say once each minute. Its shaft it is connected to operate a two lobedcam ii, the lobes of which are diametrically disposed and simultaneouslybecome effective to close the normally open switches Sc, Sfia. Thismotor, in the specific form illustrated, may be presumed to producerotation of its cam ll, one revolution every 60 seconds, and the camlobes are of such circumferential extent as to close and hold closed theswitches S0, S6. for intervals of three seconds each, so that in acomplete rotation of the cam each switch is closed during two periods ofthree seconds each and is opened during two periods of 27 seconds each.

Motor unit C is like motor unit B and is also unidirectional. It isoperated only intermittently, each time a correcting influence upon theboiler is required or called for. Its shaft I8 is connected to operate acam l9 having high and low lobes 20, 2 i, each approximately incircumferential extent, the lobes of said cam actuating the severalswitches S5, S7, Sm. Motor C and cam I! also may be assumed to be soarranged as to produce a 180 rotation of cam is in 30 seconds. In eiiectthis is a half revolution mechanism, because to produce any correctinginfluence called for, the

switches and circuits are so arranged and operated as to cause the camto start, to turn 180, and then to stop, pending another operation.

Switch S1 is the main switch. It may be located. on the door of thehousing (not shown) enclosing motors B and C and their cams and some ofthe other switches, the operating knob for switch S1, of course, beingaccessible from the outside of the door. The blade of the switch,connected by conductor 22 to terminal L1, may be moved to any of fourpositions, which here for convenience are marked as follows:

Oil, the position in which the switch is open, deenergizing allcircuits.

Open, the position in which the switch di-- rectly connects motor A toL1 by conductor 23 to cause it to turn in a direction to open the damper15. The motor, of course, is provided with a ground wire ."l connectingit by lead conductor 25 to In.

Closed," the position in which the switch conmeets the motor A byconductor 25 to L1, to turn in a direction to close damper i5.

Auto." the position inwhich the switch (51181- gizes all of the circuitsfor automatic control of the damper by variations in boiler pressure, ina manner to be described.

Switch S2 is manually operated and is in a conductor 21 from Auto tomotor B, which in turn is connected by conductor 28 to L2. When thisswitch is closed the motor 18 operates continu- .ously, with operationof the cam H as before described.

, a conductor 23 which connects the blade of switch S4 to the conductor21 and L1. This switch and switch S1 may be located either inside oroutside of the housing, as desired.

Switch S4 is a snap switch stable in either of two positions engagingone or the otherof its two contacts I and r. It is operated by themovable abutment l3, the position of which is sensitive to boilerpressure. The switch blade, of course, is moved in one direction byincrease in boiler pressure and in the opposite direction by a suitablespring 30.

Contact 1- of switch S4 is connected by conductor 3| to the blade ofswitch S6, by conductor 32 to the contact l-of switch S5, and byconducto 33 to the contact I of switch S'z.

Contact l of switch S4 is connected by the conductor 34 to the contact1' of switch S5, by the conductor 35 to the contact 1' of switch Sn, andby conductor 36 to the blade of switch 86a.

The blade of switch S5 is connected by conductor 31 to one terminal ofmotor C, the opposite terminal being connected by conductors 38, 24 and25 to L2. The operating arm of the blade of this switch is provided witha member 39 yieldably held in contact with the lobes of cam i9 by spring40.

Switch Se, normally biased to open position, cooperates with switch S1.'Its contact is connected by conductor 4| to the contact r of switch S1.

- 33 to contact I and the blade of switch S1 and by conductors 43 and 26to motor A, operating said motor in a direction to close the damper l5.This operation'continues untilthe cam is has been rotated 180. or for 30seconds, completing a substantial portion of total possible adjustmentof the damper l5. Thereupon, the blades of all three of switches S5, S7and Sm are moved to their opposite positions.

Usually, in any concrete embodiment of the invention the cam l9 and itslobes and the mechanical connections to the several switches are soarranged, and the switches themselves are of such character, that themotion of switches S1 and Sn. is completed before that of switch S5.insuring full 180 rotation of cam is during each operation.

Since the position of switch S: has changed.

- this switch is now open at contact 1 and closed at 1'. Current cannotflow continuously to motor A by way of conductor 43. However, it is nowsupblade of switch S1, to the same conductor 43.

Switch See. similar to Sc, cooperates with switch Sn. Its contact isconnected by conductor 42 with the contact I of switch Sn.

The blade of switch S7 is connected by conductors 43, 26, to motor A, tosupply current for operating it in the damper closing direction.

The blade of switch Sn is likewise connected by conductors 44, 23, tomotor A, for supplying current to operate it in a direction to open thedamper l5.

Switches S1 and Sm are arranged for simultaneous operation by the lobesof cam l9. As shown their arms are connected to a member 45 held by acompression spring 46 in contact with the cam lobes,

The system described operates as follows:

Let us assume the parts in the position shown. Switch S1 is on thecontact Auto, so that the entire controlling system is connected forautomatic control of the damper l5 by variations in boiler pressure.

Switch S2 is closed, so that motor B is operating continuously, theeffect of its cam I! being to close each of the switches Sc, Se. for aperiod of three seconds during each interval of 30 seconds;

Switch S3 is closed, energizing switch S4, which we will assume has justbeen moved to its contact r as the result ofan increase in boilerpressure beyond the maximum controlling value. The damper I3 is eitheropen or is nearer open than closed position, depending upon how far itwas adjusted during the preceding operation of the control. apparatus.In any event increase of boiler pressure demands that the damper beclosed or partly closed to reduce the draft air for combustion in theparticular arrangement illustrated.

With the cam l9 and switch S5 in the positions shown, movement of switchS4 to contact 1' completes a circuit from L1 by way of switch S1,conductors 21, 29, switch S4, conductor 32, contact 1 and the blade ofswitch S5, and conductors 31, 33, 25 to L2, through motor 0, whichbegins to rotate in the direction of the arrow. Switch S1 Therefore,every time the switch S6 is closed (for three seconds during every 30seconds) a further impulse is given to motor A and slow or moreprotracted adjustment of the damper I5 toward closed position proceeds.In the arrangement shown, this protracted later portion of the adjustment is by steps, as in said prior patent, although it may becontinuous, though very gradual, as before described.

The correcting influence upon damper I5 continues until the damper isfully closed, when further operation of the motor is usually interruptedby suitable automatic stop mechanism (not shown and forming no part ofthis invention) or it may proceed to a point short of full adjustmentuntil a reverse correcting influence is demanded, as by a reduction insteam pressure below the minimum value required for operation of thecontrol system.

If operation of motor A is stopped by automatic stop mechanism, thecontrol system lies dormant awaiting a correcting influence in theopposite direction.

Whenever an opposite correction is required, as by reduction in steampressure, requiring opening of the damper, the eilect of the reducedsteam pressure moves switch S4 to its opposite position on contact I.The circuit to motor C is now completed from switch s; by way ofconductor 34, switch St and conductor 31. Cam l9 begins to rotate andturns through another and then stops. While it is turning, current issupplied to motor A by way of conductor 35 switch S71; and conductors 44and 23, rotating the motor A in the opposite direction continuouslyuntil cam l9 completes its, 180 of motion. The effect is to produce animmediate substantial adjustment of the damper l5. Thereupon switchesS5, Stand onds) by intermittent closing of switch S6 by the cam ll. Thiseffects the more protracted adjustment of the damper as before.

The operation of the present system is well illustrated by the diagram,Fig. 2, in which the horizontal abscissas represent time in minutes andthe vertical ordinates represent boiler pressure. The wavy line Mrepresents variations in boiler pressure incident to boiler operation.The Jagged line N represents motion of the controlling motor A anddamper IS in one direction or the other. as the result of operation ofthe control system.

It is assumed that the boiler pressure is to be maintained at 100 poundsand that variation of such pressure by a halt pound above or belownormal will produce operation in one direction or the other of themovable abutment l3 and the switch S4 which it controls. It is assumedthat at the beginning of the operation represented, the damper is closedor partly closed and the boiler pressure is falling. When the pressureline drops below 99.5 the control system responds by promptly moving thedamper a substantial amount toward open position, such operationcontinuing for seconds, as indicated at 0. Then, when the cam i5 hascompleted its 180 movement, further more gradual or protracted adjustment of the damper continues by a series oi. steps, as represented at P.The boiler pressure finally begins to rise, crosses the mean or normalvalue of 100 and when it exceeds 100.5 produces similar immediate andprotracted adlustments oi the damper in the opposite direction, as at(2!.

Thus, whenever a, correcting influence is called for it is immediatelyproduced to a material eittent, depending upon the time value of cam i9,and in the present instance possibly more than of the total possiblecorrection, although the invention is not limited to any particularpropor tion. Thereafter the correcting influence continues more slowlyor gradually until the boiler pressure begins to vary in the oppositedirection and finally produces its own call for correction in theopposite direction.

The net effect of operation of the entire system is .to reduce themaximum swing or variation. in boiler pressure from a total of six ormore pounds, when the correcting influence is produced entirely byprotracted control, as in said prior patent, to a maximum of two pounds,according to the pres-- ent invention.

Although motor A always rotates at the same speed, expressed in R. P.IVL, nevertheless it is so controlled that over its full range ofoperation in one direction or the other the rate of opera" tion of boththe motor and the damper which it controls is considerably greaterduring the initial adjustment than during the final adjustment. theexample given, assuming that motion oi." the damper from full open tofull closed position requires 180 of angular travel, accomplished bymotor operation for seconds, the initial prompt adjustment is at therate of of travel in 30 seconds. The final more protracted adjustment,however, is much slower at the rate oi 90 of travel in 300 seconds,because the motor operates for only 3 seconds in every 30 seconds.

The line R on the chart, Fig, 2, represents the load line of the boilerin horsepower per hour.

It may be assumed in this boiler, that the normal load is horsepower.The diagram indicates a rise in load from 15 minutes to 24 minutesfollowed by a decrease to normal at 29 minutes.

Upon any such variation in normal load, up or down, the initial rapid,substantial adjusting effect, when correction is demanded, is continuedfor 30 seconds, as before, under the control of cam i9. However, theslower, protracted control persists for a longer period or is'reduced toa shorter period, to accommodate the control mechanism to variations inload, as indicated by the line N during the interval mentioned item 15to ill) Bil

(ill

diate position. Whatcvc 8 29 minutes. The boiler pressure, however, ismaintained at the mean value or 100 pounds, plus or minus pound, asbefore.

The main purpose of the invention, of course. is to control the rate ofproduction of heat, whether the heat is used merely for heating purposessuch as for heating air, water or the like, or for the production ofpower, such as in a steam boiler, When the heating unit is of thelectrical form the control-system will either very or adjust resistanceor throw one or more heaters or heat ing elements into or out ofoperation. W it controls a heat producing unit utilizing solid it cancontrol dampers or mo :1 l producing air supply, o fuel. When used to coo7. ploying liquid or gaseous time u to control fuel valves or theports, or dampers or mot ducing air flow, as will c It should also benot.- eratlve, as described. ti l 1 device to be regulated lyiu in itstwo extreme positi.

correcting influence is col in the proper direction, in too .1 asubstantial adjustment to 5D or more percent 01" the t ment, and'secondby a m' ment until total adjustmcu producing element become adjustmentis produced crates equally well in whether more or less steam i oi,boiler operation. Other advantages ol' parent to those skilled "What Iclaim is:

l. Control means for o comprising an adjustalo the rate of heatproduction by said unit, an ac sting motor therefor, governing means,sensitive to and actuated by variations in g function of said unit, anelectric rcuit for said motor having two branches each including switchmeans, a cyclic controller lor closir. the switch means in the first ofsaid branches and maintaining it closed for a sufficient period to causesaid motor to eflect a substantial. proportion oi the total possibleadjustment oi device, means governed by said governing means startingand stopping the cyclic controller, means open atcd by said controllerfor closing; the switch means in the second branch. o1? said circuitwhen the cyclic controller comes to rest, an independent switch in saidsecond branch, and continuously operating means for-intermittentlyclosing said independent switch to cause said motor to produceintermittent adiustment oi, said device after its said substantialadjustment.

2. Control means for a heat producing, unit, comprising an adjustabledevice for regulating the rate of heat production by said unit, an actuating motor therefor, governing means sensi tive to and actuated byvariations in an operating function of said unit, a continuouslyoperatin control motor, control means operated thereby and operativelyconnected to said actuating motor and adapted when eilective thereon tointermittently cause actuation thereof, and a cyclic controller arrangedwhen energized to start and stop and operatively connected to saidgoverning means to be governed and thereby rendered effective thereby,said cyclic controller being also so operatively connected to saidactuating and control motors that during its cycle it causes andmaintains operation of said actuating motor and at the conclusion 0! itscycle renders said control motor eflective upon said actuating motor.

3. Control means for a heat producing unit,

comprising an adiustable device for regmatms the rate or heat productionby said unit, an actuating motor therefor, governing means sensitive toand actuated by variations in an operating function 01' said unit, acontinuously operating motor, control means operated thereby andconnected to said actuating motor and adapted when eflective thereon tointermittently cause actuation thereof, control means governed by saidgoverning means and arranged to render said continuously operating motoreffective upon said actuating motor, said control means includingcyclically operating means arranged to start and stop and adapted duringits cycle to cause operation of said actuating motor independently ofsaid continuously operating motor and to delay effective operation ofsaid actuating motor by said continuously operating motor pendingcompletion of the cycle.

GEORGE A. SHORT.

